Within the field of semiconductor circuits, certain categories of circuitry require a reliable operation over a range of temperatures. One circuit that may be used to provide a constant reference source is a bandgap voltage reference.
Bandgap voltage reference circuits are designed to sum two voltages with opposite temperature slopes. One of the voltages is a Complementary-To-Absolute Temperature (CTAT) voltage typically provided by a base-emitter voltage (VBE) of a forward biased bipolar transistor. The other is a Proportional-To-Absolute Temperature (PTAT) voltage typically derived from the base-emitter voltage differences of two bipolar transistors operating at different collector current densities. When the PTAT voltage and the CTAT voltage are summed together, the summed voltage is at a first order temperature insensitive.